This is commonly known as the tennis ball cactus. It is the most coveted plant among collectors, super rarely on offer and mostly when it is, it is only the seeds that are available. This plant is super rare in New Zealand and most plants reside in private collections. On offer is a graft consisting of 1/4 of a ball. This plant is extremely slow growing hence the price. This is grafted onto san pedro which is a strong rootstock and should allow this plant to grow a little faster than it would on its own roots. Plants come in a 8cm nursery pot. 

Note: This is a one off plant as they are super slow to grow. The plant in the picture is what you are getting. The last picture is an example of that this plant should look like when it is mature.

Watering

Allow the plant to dry out between waterings. Do not allow the plant to sit in water. Feed during active growing season with fertiliser at label rates.

Lighting 

Enjoys full sun but protect plant from harsh afternoon sun as the heat can kill this plant.